1. Field of the Invention
The present invention relates to wet strength resin compositions and methods of making the same and particularly to improved polyamine-epichlorohydrin wet strength resins.
2. Description of Related Art
Polyamine-epichlorohydrin resins have been used as wet strength resins for paper since the early 1950's. Such resins are cationic and are particularly useful because they are formaldehyde-free and develop wet strength at neutral or alkaline pH values.
One of the drawbacks associated with the use of polyamine-epichlorohydrin resins is the emission of harmful chlorinated compounds into the water systems of pulp and paper mills. These chlorinated compounds, including 1,3-dichloro-2- propanol, epichlorohydrin and 1-chloro-2,3-propanediol, are usually discharged into the effluent waste water systems because they are only partially substantive to cellulose pulp fibers. The permissible amounts of these chlorinated compounds is decreasing and therefore efforts have been made to reduce the amounts of these materials.
Stephen A. Fischer et al, U.S. Pat. Nos. 5,116,887 and 5,120,773 disclose methods of preparing polyamine-epichloro-hydrin resins under conditions which reduce the amount of volatile organic compounds. In particular, a polyamine solution and epichlorohydrin are combined to form a reaction mixture having a relatively high E/N ratio of from about 1.0 to about 1.4 which is reacted at a relatively high temperature of 50.degree. to 80.degree. C.
European Patent Publication No. 0 508 203 discloses low chlorine component resins produced by the reaction of an epihalohydrin and a polyalkylene polyamine in which the E/N ratio is relatively low (i.e. less than 1.0) and the reaction temperature is also relatively low (i.e. less than 60.degree. C., typically about 25.degree. to 45.degree. C.
A low E/N ratio of 0.6 to 1.08 and a low reaction temperature of about 5.degree. to 30.degree. C. have been used to reduce chlorides in an aminopolyamide-epichlorohydrin resin as disclosed in Devore et al. U.S. Pat. Nos. 5,239,047 and 5,189,142.